1 //! lint on blocks unnecessarily using >= with a + 1 or - 1
6 use utils::{snippet_opt, span_lint_and_then};
8 /// **What it does:** Checks for usage of `x >= y + 1` or `x - 1 >= y` (and `<=`) in a block
11 /// **Why is this bad?** Readability -- better to use `> y` instead of `>= y + 1`.
13 /// **Known problems:** None.
28 "instead of using x >= y + 1, use x > y"
31 pub struct IntPlusOne;
33 impl LintPass for IntPlusOne {
34 fn get_lints(&self) -> LintArray {
35 lint_array!(INT_PLUS_ONE)
48 #[derive(Copy, Clone)]
55 #[allow(cast_sign_loss)]
56 fn check_lit(&self, lit: &Lit, target_value: i128) -> bool {
57 if let LitKind::Int(value, ..) = lit.node {
58 return value == (target_value as u128);
63 fn check_binop(&self, cx: &EarlyContext, binop: BinOpKind, lhs: &Expr, rhs: &Expr) -> Option<String> {
64 match (binop, &lhs.node, &rhs.node) {
65 // case where `x - 1 >= ...` or `-1 + x >= ...`
66 (BinOpKind::Ge, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _) => {
67 match (lhskind.node, &lhslhs.node, &lhsrhs.node) {
69 (BinOpKind::Add, &ExprKind::Lit(ref lit), _) if self.check_lit(lit, -1) => {
70 self.generate_recommendation(cx, binop, lhsrhs, rhs, Side::LHS)
73 (BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) if self.check_lit(lit, 1) => {
74 self.generate_recommendation(cx, binop, lhslhs, rhs, Side::LHS)
79 // case where `... >= y + 1` or `... >= 1 + y`
80 (BinOpKind::Ge, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs))
81 if rhskind.node == BinOpKind::Add =>
83 match (&rhslhs.node, &rhsrhs.node) {
84 // `y + 1` and `1 + y`
85 (&ExprKind::Lit(ref lit), _) if self.check_lit(lit, 1) => {
86 self.generate_recommendation(cx, binop, rhsrhs, lhs, Side::RHS)
88 (_, &ExprKind::Lit(ref lit)) if self.check_lit(lit, 1) => {
89 self.generate_recommendation(cx, binop, rhslhs, lhs, Side::RHS)
94 // case where `x + 1 <= ...` or `1 + x <= ...`
95 (BinOpKind::Le, &ExprKind::Binary(ref lhskind, ref lhslhs, ref lhsrhs), _)
96 if lhskind.node == BinOpKind::Add =>
98 match (&lhslhs.node, &lhsrhs.node) {
99 // `1 + x` and `x + 1`
100 (&ExprKind::Lit(ref lit), _) if self.check_lit(lit, 1) => {
101 self.generate_recommendation(cx, binop, lhsrhs, rhs, Side::LHS)
103 (_, &ExprKind::Lit(ref lit)) if self.check_lit(lit, 1) => {
104 self.generate_recommendation(cx, binop, lhslhs, rhs, Side::LHS)
109 // case where `... >= y - 1` or `... >= -1 + y`
110 (BinOpKind::Le, _, &ExprKind::Binary(ref rhskind, ref rhslhs, ref rhsrhs)) => {
111 match (rhskind.node, &rhslhs.node, &rhsrhs.node) {
113 (BinOpKind::Add, &ExprKind::Lit(ref lit), _) if self.check_lit(lit, -1) => {
114 self.generate_recommendation(cx, binop, rhsrhs, lhs, Side::RHS)
117 (BinOpKind::Sub, _, &ExprKind::Lit(ref lit)) if self.check_lit(lit, 1) => {
118 self.generate_recommendation(cx, binop, rhslhs, lhs, Side::RHS)
127 fn generate_recommendation(
134 ) -> Option<String> {
135 let binop_string = match binop {
136 BinOpKind::Ge => ">",
137 BinOpKind::Le => "<",
140 if let Some(snippet) = snippet_opt(cx, node.span) {
141 if let Some(other_side_snippet) = snippet_opt(cx, other_side.span) {
142 let rec = match side {
143 Side::LHS => Some(format!("{} {} {}", snippet, binop_string, other_side_snippet)),
144 Side::RHS => Some(format!("{} {} {}", other_side_snippet, binop_string, snippet)),
152 fn emit_warning(&self, cx: &EarlyContext, block: &Expr, recommendation: String) {
153 span_lint_and_then(cx, INT_PLUS_ONE, block.span, "Unnecessary `>= y + 1` or `x - 1 >=`", |db| {
154 db.span_suggestion(block.span, "change `>= y + 1` to `> y` as shown", recommendation);
159 impl EarlyLintPass for IntPlusOne {
160 fn check_expr(&mut self, cx: &EarlyContext, item: &Expr) {
161 if let ExprKind::Binary(ref kind, ref lhs, ref rhs) = item.node {
162 if let Some(ref rec) = self.check_binop(cx, kind.node, lhs, rhs) {
163 self.emit_warning(cx, item, rec.clone());